These inventions relate to interactive cable antenna television (CATV) systems (also known as broadband networks) for distributing television programs, radio programs, and data (e.g. equipment control commands, equipment status information, telephone data, and computer data) through a cable network to customers and for receiving data through the cable network back from customers. In such systems optical information signals including programs and data are distributed through an optical cable network or tree from a head-end to local nodes and customer return information signals including data are collected through another optical cable network or tree from the local nodes back to the head-end. More specifically, the invention is related to the status and control signals used for operating such a system in an efficient manner.
In a modern CATV system, lasers are used for converting electrical signals into optical signals which are transmitted through optical cables. Also, photo detectors such as photo diodes are used for converting optical signals into electrical signals to receive the signals from the optical cables. Prior to electrical to optical conversion, the electrical signals need to be amplified with carefully controlled gain in order for the laser to provide the maximum available bandwidth and to minimize error rates. Also, after optical to electrical conversion, the electrical signals need to be amplified for transmission through a coaxial cable network.
At the head-end of a CATV system a coaxial cable network provides electrical signals including a multitude of television program streams and data streams (such as telephone calls, equipment control commands, and computer data) which are combined together into a forward information stream which is used to modulate a laser for transmitting the information stream through a forward optical cable network as an optical signal for distribution to a multitude of nodes. At the nodes the optical signal is used to modulate the current through an photo detector to convert the optical signal into a forward electrical signal.
The forward electrical signal is transmitted from the nodes through a local coaxial cable network to a multitude of customer interface units (CIUs). The CIUs provides the forward information signals to television, telephone, and computer equipment, and receive return data streams from the telephone and computer equipment. The CIUs transmit the return signals back through the coaxial cable network to the nodes. The nodes include diplexers to separate the return signals out from the forward signals. The nodes use the separated return signals to modulate a return laser for transmitting the return data stream through a return optical cable network as an optical signal to the head-end. The head-end provides the return signals to telephone and computer equipment at the head-end.
In CATV systems there are stringent requirements for minimum signal strength, minimum signal to noise ratio, and maximum signal distortion at the CIUs. These requirements effectively limit the distance that the customers can be serviced through the CATV system. Noise and distortions are inherent in the laser transmitters and these limit the power of the lasers and frequencies used for optical transmission. Rayleigh back scattering is due to localized variations in the density of the optical fibers and additional back scattering is due to components in the optical cable such as connectors, optical isolators, splices, and detectors which reflect light. Back scattering and reflection result in light traveling back into the laser and tends to modulate the laser and to interfere with the transmitted light which results in noise. In the optical cable, light is absorbed so that the signal strength attenuates with distance (typically about 0.4 db per km). The optical detectors of the receivers continually produce random noise which is mixed with the weakened signal so that signal to noise ratio is further reduced. Currently in analog systems, optical cable lengths are limited to approximately 50 miles due to these reductions in the signal to noise ratio.
In the coaxial portion of the system, random noise is introduced by the CIUs and also by leakage from external electromagnetic signal sources into the cables. Amplifiers are provided in the coaxial system if required to maintain a high signal strength in remote parts of the coaxial system, so that the effects of this random noise on signal strength to noise ration is limited. However the amplifiers add to the noise. The noise due to the optical portion of the transmission and the noise due to the coaxial portion of the system are combined in the signal and the signal has to meet the stringent signal to noise requirements described above.
Those skilled in the art are referred to U.S. Pat. No. 5,435,868 to Blauvelt.
The above citations are hereby incorporated herein in whole by reference.
A node of a CATV system includes apparatus for providing a reference signal and the head-end of the CATV system includes apparatus to allow the presence of the reference signal to be detected. The reference signal provider and detector allow the correct operation of the return paths from the nodes to the head-end to be verified. The head-end includes measurement apparatus to allow the strength of the reference signal to be determined and the signal strength of the return signal to be adjusted at the head-end so that the signal strength of all the return paths are made approximately equal (they are aligned). Control apparatus of the head-end includes software to automatically align the return signal path by sending control signals to the optical receivers of the head-end which include controllable gain adjustment apparatus.
The head-end control apparatus includes software for providing control signals to the nodes including signals for turning on and turning off the reference signal provider and the nodes include control apparatus for detecting the control signals and turning the reference signal provider on and off depending on the control signals from the head-end. The head-end control apparatus includes user input means for selecting a node or nodes and for addressing or specifically routing the control signals from the head-end to only the selected node or nodes. In order to verify the correct operation of both the forward and return information networks, the head-end controller is programmed for selecting a node, sending a command to change the reference signal (turn the reference signal of the selected node on or otherwise changing the signal in such a way that the change can be automatically detected) and detecting the presence of the reference signal. In addition, the head-end control apparatus includes programmed apparatus for providing control signals to control the amplitude and/or frequency of the reference signal; the node control apparatus of the head-end is adapted for controlling the amplitude of the reference signal and/or the frequency of the reference signal depending on the control signals from the head-end control apparatus; and the head end includes apparatus for automatically detecting the presence, amplitude and frequency of the reference signal.
The control apparatus of the head-end includes programmed apparatus for requesting status information about node equipment. The node includes monitoring apparatus for detecting the status of various equipment within the node such as the bias current of the laser transmitter, the output power of the laser transmitter, faulted conditions of the laser transmitter. The monitoring apparatus generates monitor status signals indicating the status of the equipment in the node which are transmitted to the node control apparatus, and the node control apparatus sends node status signals to the head-end control apparatus depending on the monitor status signals and status query command signals.
The head-end controller may include a user interface including a keyboard and mouse for user input and a display and printer. The user can enter commands to align the return distribution system or select a node and specify control signals to control equipment in the node such as: to turn the reference signal on or off, to turn the laser transmitter on or off, to transmit the status of other equipment in the node, to verify the correct operation of the distribution networks. The display may list available commands, equipment status information relevant for choosing the command of effected by executing such commands, and the status of the reference signals from the nodes.
Other alternatives and advantages of the inventions herein will be disclosed or become obvious to those skilled in the art by studying the detailed description below with reference to the following drawings which illustrate the elements of the appended claims of the inventions.